Method for blow molding metal containers

ABSTRACT

A method is disclosed for pressure forming a metal preform including shock annealing of the preform and subsequently preheating the preform prior to pressure forming. Shock annealing may be carried out as differential shock annealing in which different regions of the preform are annealed to different degrees. Preheating may be carried out by differentially preheating, optionally shock preheating, different regions of the preform for preheating at least those regions of the preform which will be subject to elevated expansion during pressure forming. Shock annealing by induction heating can lower energy consumption, reduce processing times and allow for larger expansion of the preform.

This application is a continuation application of U.S. patentapplication Ser. No. 14/667,139, filed Mar. 24, 2015. This applicationclaims priority under 35 U.S.C. § 119(e) to U.S. Provisional PatentApplication Ser. No. 61/970,103, filed Mar. 25, 2014, which isincorporated herein in its entirety by reference.

The invention relates to methods and apparatus for forming metalcontainers or the like, utilizing internal fluid pressure to expand ahollow metal preform or workpiece against a die cavity, to produce acontainer having a contoured shape.

Metal cans used for beverages and the like are either one-piece bodies,or bodies open at one or both ends and closed at those top and bottomends by separate parts. Conventional cans generally have simple uprightcylindrical sidewalls. For reasons of aesthetics, consumer appeal orproduct identification, it may be desired to impart the can with a morecomplex shape. For example, it may be desired to provide a metalcontainer in the shape of a bottle rather than an ordinary cylindricalcan shape, or to provide an ergonomically shaped bottle akin to alreadyavailable shaped plastic or glass bottles.

Aluminum containers have been conventionally formed using variousdifferent approaches. In one approach, a progressive series of dies isused to draw, re-draw or shape a flat plate or metal sheet into apreform in the shape of a cylinder with a closed bottom. The preform canthen be provided with a top lid to form a can or drawn by and neckedusing necking dies into a bottle shape. The container open end is curledand can be threaded for mounting a closure cap. In another approach, apreform is formed from a metal sheet that is rolled and welded to form acylinder with opposite open ends, welding a bottom onto the cylinder andeither closing the top end or drawing and necking the top end into abottle shape.

In an alternative aluminum container forming method, a preform is impactextruded from an aluminum slug, as described in WO 2013040339 A1 byStiles et al. Impact extrusion is a process utilized to make metalliccontainers and other articles with unique shapes. The products aretypically made from a metal slug comprising steel, magnesium, copper,aluminum, tin or lead. The container is formed inside a confining diefrom a cold slug which is impacted by a punch. The force of the punchimpact deforms the metal slug around the punch and forces the slugmaterial backwards between the punch and the die wall, opposite to thedirection of punch movement. After the initial preform shape, a cylinderwith closed bottom, is created, the preform is removed from the punchwith a counter-punch ejector. Necking, or necking and shaping, tools areused to form the preform into a preferred shape. Embossing tools mayalso be used to generate three-dimensional structures within thecontainer wall.

Impact extruded containers include aerosol containers and other pressurevessels, as well as traditional aluminum beverage containers. Aerosolcontainers and pressure vessels generally require high strength and usethicker gauge materials than traditional aluminum beverage containers.The top end of the preform can be drawn, rolled, or necked to form abottle shape.

In the shaping methods described above, the preform is necked or shapedby mechanical means. In an alternative shaping process, the preformapproximates the final container shape and a pressurized fluid (gas orliquid) is used to expand the preform in a mold. This is generallyreferred to as pressure forming, or blow molding where pressurized gasis used. Examples of known methods of blow molding preforms intoaluminum containers are found in the publications of: U.S. Pat. No.7,107,804 dated Sep. 19, 2006; U.S. Pat. No. 6,802,196 dated Oct. 12,2004; and US Application Publication 2011/0167886 dated Jul. 14, 2011.

Pressure Ram Forming (PRF)

U.S. Pat. No. 7,107,804 discloses a special blow molding process, thepressure-ram-forming process, or PRF. In PRF, a metal container ofdefined shape and lateral dimensions is formed both by fluid pressure,applied either internally or internally and externally, and by thetranslation of a ram driven by a shaft. In the method disclosed, ahollow metal preform formed by a draw, re-draw or back extrusion processfrom a metal sheet and having a closed end, is placed in a die cavitylaterally enclosed by a die wall defining the shape and lateraldimensions of the finished container. A ram located at one end of thedie cavity is translatable into the cavity. The preform is generallycylindrical and is subjected to the fluid pressure to expand the preformoutwardly into substantially full contact with the die wall. Thisimparts the defined shape and lateral dimensions to the preform in onesingle forming step. Any stretching, bending, shaping or otherdeformation of the preform material required for transition from thepreform shape to the final shape occurs during a continuous, singleshaping operation. Thus, extreme stress may be imparted on the preformmaterial during shaping, especially for final shapes that requirebulging of the preform sidewall into an expanded shape and formation ofa relief of protruding or recessed shapes on the expanded shape. Afterthe preform begins to expand but before expansion of the preform iscomplete, the ram is translated into the cavity to deform the closed endof the preform inward.

Annealing Prior to Shaping

Containers of more complex shape can be manufactured with differentshaping methods, for example embossing, roll forming, electromagneticforming, hydroforming or pressure forming, such as thepressure-ram-forming method. However, work hardening of the preformmaterial either before or during forming of the preform, which is aresult of the strain imposed on the aluminum, can lead to integrityproblems during the subsequent shaping operation. Annealing of thepreform material to increase ductility prior to shaping can be carriedout by heating the preform.

Annealing of a metal workpiece generally involves heating the materialof the workpiece to above its glass transition temperature and below itsmelting point, and then cooling. The material is commonly maintained ata selected annealing temperature for a specific dwell time intended toallow for removal of dislocations, realignment of grains in thematerial, and subsequent recrystallization of the grains to form ahomogeneous, equiaxed grain structure. Annealing can induce ductility,soften the material, relieve internal stresses, refine the structure bymaking it homogeneous, and improve cold working properties. Afterannealing, objects must be cooled to stop the annealing process andlimit grain growth. If the material is maintained at the selectedannealing temperature past the point where recrystallization iscomplete, grain growth will occur, which is disadvantageous, since themicrostructure of the material starts to coarsen as a result, which maycause the material to lose a substantial part of its original strength.

Preforms manufactured from sheet material can be annealed to reduce theeffect of work hardening and to make the preforms more ductile. Arecovery anneal can be carried out on the starting sheet material priorto drawing of the preform, or on the preform itself, prior to theshaping step. Annealing of the preform during a can forming process forthe purpose of relaxing the material in the sheet material based preform(recovery anneal) is disclosed in CA 2,445,582 by Moulton et al.Annealing of the sheet material prior to the forming of the preform issuggested in U.S. Pat. No. 7,107,804, while relaxing of the preformmaterial prior to blow molding is disclosed in CA 2,445,582 andUS2011/0113732A1.

In all of these methods, the annealing is carried out by subjecting thestarting material or preform to externally applied heat, for example inan annealing oven or furnace. This convective heating by the externalapplication of heat (hot air, etc.), is sufficient to relax thematerial. However, annealing by convective heating is time consuming andinefficient, since a significant portion of the heat supplied may belost to the environment and not transferred to the preform. Moreover, inorder to ensure sufficient annealing of all areas of the material, thedwell time used is often longer than the time theoretically required toachieve the desired degree of anneal. This may lead to over-annealing,or to grain growth in the material being annealed, causing a progressiveloss in material strength.

The use of inductive heating for the partial annealing of preforms drawnor re-drawn from sheet material is suggested in U.S. Pat. Nos. 5,058,408and 6,349,586. Although the use of inductive heating is disclosed, onlya partial anneal of the sheet material is achieved.

Annealing of an impact extruded preform is suggested in U.S. Pat. No.6,776,270. In the container shaping method disclosed, multiple expansionsteps are used to shape aluminum containers having highly contouredsidewalls not producible with prior expansion methods. An annealingtreatment of the sidewall is carried out prior to each expansion step inorder to avoid rupture of the sidewall during the subsequent expansionstep. The annealing treatment is carried out by inductive heating of thesidewall. The preform is first partially or fully annealed (to 0temper), subjected to a first expansion, annealed again and thensubjected to a second expansion. Inductive heating is used to heat thepreform material. The multiple expansion process is required to enablean expansion of more than 23.7%. All examples are limited to drawn andironed preforms. Impact extruded preforms were not tested. Fullannealing of the drawn and ironed preforms was achieved by inductivelyheating the preform to 625° F. for 30 minutes. This process requiresmultiple shaping steps and is therefore not usable in connection withPRF.

Preheating Prior to Shaping

Independent of any annealing of the preform material, the preform canalso be preheated just prior to pressurization to make the preformmaterial more ductile and prevent cracking or structural failure of thecontainer wall. Selective preheating of different regions of the preformprior to deformation and/or expansion during the PRF process isdisclosed in U.S. Pat. No. 7,107,804. In the disclosed process, heat istransferred to the preform by contact with a heated object, for examplethe forming ram. Sectional pre-heating of the body of the preform byconvective heating between the top and bottom ends is also possible anddisclosed in US2013/0167607A1 and WO 2002087802 A.

Preheating selected regions of a pipe preform by induction heating forthe purpose of thickening the pipe wall during forming is disclosed inU.S. Pat. No. 5,992,197 by Freeman et al. However, this type ofpreheating requires the use of a continuous preform and is notapplicable for preform expansion by pressure forming.

Surface Finish

Aluminum containers generally require an interior coating or lacquer toprevent corrosion and spoiling of the contents, or for sanitary reasons.The exterior of the container generally also requires a coating fordurability, labeling, decorative appearance and marketing reasons. Theapplication of interior or exterior coatings after blow molding thecontainer into complex shapes is difficult. Since the preform generallyhas a simple cylindrical shape it is preferred to apply the coatings tothe preform before blow molding. However excessive preheating of thepreform prior to blow molding can damage those coatings.

It is an object to address at least one disadvantage of the prior artprocesses and apparatus.

SUMMARY OF THE INVENTION

During impact extrusion of a slug, significant shear stresses areimposed on the slug material. These shear stresses are much higher thanthose occurring during drawing, redrawing or back extrusion of a sheetmaterial. The dislocation density in a metal increases with plasticdeformation. The shear stresses created during impact extrusion resultin a much higher dislocation density in an impact extruded preform thanin a sheet-based preform. The higher the dislocation density, the harderthe material and the more resistant it becomes to further deformation.This effect is called work hardening. In the context of thisspecification, the term metal slug is used to define flat, beveled, ordomed discs of extrudable metal material having a circular, regular, orirregular circumference. Impact extruded workpieces are known to besubject to significant work hardening and to a very high dislocationdensity. Moreover, impact extruded preforms generally have a higher wallthickness than sheet based preforms. Therefore, an impact extrudedpreform will be subject to localized failure of the preform materialupon further deformation, especially expansion, without annealing of thepreform material. However, heating to anneal an impact extruded preformby convection is inefficient. Heating by induction required multipleannealing steps in the past, thus making impact extruded preformsimpractical for use in PRF.

Shock Annealing

The inventors have now surprisingly discovered that an impact extrudedpreform can be used in the PRF process, wherein the preform material isshock annealed prior to expansion, and that the use of shock annealingobviates the need for multiple annealing steps.

Shock annealing in the context of this description is defined as rapidlyheating the metal material to be annealed to achieve a temperature risein the material of at least 120° C./sec. The rapid heating is carriedout to achieve a preselected final annealing temperature in the range of65%-98% of the melting point temperature of the metal. A temperaturerise of at least 150° C./sec was found advantageous, or at least 200°C./sec, for example 235° C./sec to 245° C./sec. After sufficient heatingtime to reach the preselected final annealing temperature, the heatingis stopped and the material is allowed to cool. Shock annealing is mostadvantageously achieved by using inductive heating. Advantageous resultsare achieved with an electromagnetic field of a power density of 25 to100 W/cm² of preform sidewall surface. Power densities in the range of40 to 90 W/cm² have been found advantageous, for example 86 W/cm². Thismay be achieved with a power input into the induction coil in the rangeof 10 kW to 20 kW, for example 15 kW. Treatment times may lie in therange of 0.3 to about 4 seconds, advantageously in the range of 0.8 to2.5 seconds, for example 2 seconds.

In one aspect, the invention provides a method of shock annealing ametal preform by inductively heating the preform material by generatingan electro-magnetic field and exposing the preform to theelectro-magnetic field to generate a temperature rise in the preformmaterial of at least 120° C./sec to reach an annealing temperature inthe range of 65%-98% of the melting point temperature of the preformmaterial. In certain embodiments, a temperature rise of 220-250° C./sec,for example 235-245° C./sec, is generated in an aluminum preform toreach an annealing temperature of about 500-520° C., for example 510°C., which equates to about 90% of the melting point temperature, inabout 2 seconds.

In the context of this specification, the term electro-magnetic fieldrefers to a field generated by passing an alternating current (inductivecurrent) through a conductor, advantageously in the shape of a coil. Theterm metal preform in the context of this specification includes apreform made of steel, magnesium, copper, aluminum, tin or lead, oralloys thereof, and formed from sheet material by a draw, re-draw, deepdraw, machining, casting, or back extrusion process, or formed by impactextrusion from a slug. The term aluminum in the context of thisspecification includes substantially pure aluminum as well as aluminumalloys of for example the 1000, 2000, 3000, 4000, 5000, 6000, 7000 or8000 Series, for example 1000 Series or 3000 Series Alloys, such as1070, 1050, 1100 and 3207 Alloys.

The penetration depth of the electro-magnetic field into the material tobe annealed is influenced by the frequency of the inductive current usedto generate the electro-magnetic field for the induction heating. Lowerfrequencies provide deeper penetration, whereas higher frequenciesresult in shallower penetration into the material. The frequency of thealternating current used for generation of the electro-magnetic fieldalso influences the efficiency of the heating, with frequency andefficiency being inversely related. Although lower frequenciestheoretically benefit both penetration and efficiency, an increase inheating efficiency also increases the risk of localized overheating ofthe material due to tolerances in the material thickness. Frequencies inthe range of 10 kHz to 600 kHz can be used in certain embodiments of thepresent invention, with frequencies in the range of 100 kHz to 400 kHz,or 200 kHz to 300 kHz, for example 300 kHz, being advantageous to reducelocalized overheating.

The inventors have further surprisingly discovered that, despite thesignificant dislocation density in the material of an impact extrudedpreform, an impact extruded preform that is shock annealed as describedabove, optionally advantageously including differentially shock annealedregions, can be successfully used for forming with the PRF process. Theterm differentially shock annealed regions as used in this disclosuredefines adjacent regions of the preform which differ in the degree ofannealing, wherein the degree of annealing can range from partialannealing to full annealing, as long as those regions expected to besubject to the largest expansion or deformation during subsequentshaping, have been substantially fully annealed. The inventors havefound that substantially fully shock annealing only those regions of thepreform which are subject to elevated strain during molding issufficient for most embodiments. This can speed up the forming processand reduce power consumption.

In another aspect, the invention provides a method of differentiallyshock annealing a metal preform by inductively shock annealing thepreform material in at least one region to a lesser degree than in theremainder of the preform material, which remainder is inductively heatedto achieve a temperature rise in the material of at least 120° C./sec toreach an annealing temperature in the range of 65%-98% of the meltingpoint temperature of the metal.

In a further aspect, the invention provides a differentially shockannealed metal preform that has been impact extruded from a metal slugand subjected to differential shock annealing as described above.

Preheating

The inventors have also surprisingly found that, subsequent to annealingof the preform, a differential preheating of adjacent regions of thepreform, wherein elevated three-dimensional deformation during the PRFprocess will occur, can assist in the creation of smaller deformationradii and higher three-dimensional relief features, due to the regionsof less or no preheating providing a higher resistance to deformationthan those substantially fully preheated. Preheating can be mosteffectively achieved by shock preheating with induction. Shockpreheating in the context of this description is defined as rapidlyheating the metal material to be preheated to achieve a temperature risein the material of at least 120° C./sec, and to reach a final preheatingtemperature in the range of 100° C. to 300° C., or 150° C. to 250° C.,for example 200° C.

In a further aspect, the invention provides a method of differentiallypreheating a previously differentially shock annealed or substantiallyfully shock annealed preform by inductively shock preheating any regionsof the preform which will be subject to elevated deformation stressduring subsequent blow molding.

Molding Process

In yet another aspect, the invention provides a method of making amolded metal container of a desired shape from a preform having acylindrical body with an open end and a closed end, for example apreform having been impact extruded from a metal slug. The methodincludes the steps of shock annealing the preform prior to pressurizingby inductively heating the preform material to achieve a minimumtemperature rise in the material of at least 120° C./sec, advantageouslyat least 150° C./sec, for example at least 200° C./sec, or 235° C./sec,to reach an annealing temperature in the range of 65%-98%, for example90%, of the melting point temperature of the metal; fluid pressureforming the annealed preform in a shaping die or mold with a die cavitydefining the desired shape; pressurizing the preform to expand thepreform into contact with the die cavity and impart the desired shapeonto the preform; and removing the resulting molded container from thedie. For aluminum or aluminum containers, the temperature rise can befor example about 250° C./sec.

The terms die, mold, shaping die and shaping mold are interchangeablyused throughout this specification and all define the structure in whichthe preform is subjected to pressure forming.

In still another aspect, the invention provides a method of fluidpressure molding a metal container of a desired shape from a preformhaving a cylindrical body with an open end and a closed end, for examplea preform having been impact extruded from a metal slug, the methodincluding the steps of differentially shock annealing the preform priorto pressurizing by inductively heating the preform material in at leastone region to a lesser degree than the remainder of the preform materialwhich remainder is inductively heated to achieve a temperature rise inthe material of at least 120° C./sec, advantageously at least 150°C./sec, for example at least 200° C./sec, or 235 to 245° C./sec to reachan annealing temperature in the range of 65%-98%, for example 90%, ofthe melting point temperature of the metal; fluid pressure forming theannealed preform in a die with a die cavity defining the desired shape;pressurizing the preform to expand the preform into contact with the diecavity and impart the desired shape onto the preform; and removing theresulting molded container from the die.

In yet a further aspect, the invention provides a method for fluidpressure molding a metal container of a desired shape from a preformhaving a cylindrical body with an open end and a closed end, for examplea preform having been impact extruded from a metal slug, the methodincluding the steps of differentially preheating a previously shockannealed or differentially shock annealed preform prior to pressurizingby inductively preheating regions of the preform which will be subjectto elevated deformation stress during subsequent fluid pressure forming;fluid pressure forming the annealed preform in a die with a die cavitydefining the desired shape, the preform being placed in the die eitherbefore or after preheating; pressurizing the preform to expand thepreform into contact with the die cavity and impart the desired shapeonto the preform; and removing the resulting molded container from thedie.

In addition, the inventors have discovered that a preform with regionsof variable wall thickness can be successfully induction heated by shockheating (shock preheating or shock annealing) each region individually,since this will avoid the significant and undesirable local temperaturespikes generated when regions of different wall thickness are subjectedto a uniform electro-magnetic field.

Due to field strength variations in an electro-magnetic field used forinduction heating (for shock annealing or shock preheating purposes)heat generation through induction may be locally variable, which canlead to localized temperature spikes within the preform material.Although the overall field strength can be lowered to avoid exceeding adesired temperature, doing so increases the heating time and conductivelosses and expands the region of the preform which is heated. Thus,selectively and uniformly heating only limited regions of the preform toa specific temperature is difficult. However, the inventors of thepresent application have now surprisingly discovered that energyconsumption can be further reduced and the inductive heating of thepreform limited to more precisely defined, smaller regions of thepreform, by moving the electro-magnetic field in relation to thepreform. That means the preform can be moved within or through thefield, or the field can be moved along the preform, or both.

By moving the field relative to the preform, localized strengthvariations in the field no longer create localized temperature spikes,since all regions of the preform subjected to the moving field aresubjected to all field strength variations. Moreover, the movable fieldallows for the localized shock heating of selected regions withoutheating adjacent regions by switching the field on and off duringmovement, which enables differential annealing and/or differentialpreheating of the preform.

By movement of the electro-magnetic field over the preform, it isachieved that only the region of the preform subjected to the field atany given time is inductively heated, while other regions of the preformare not. That allows for a much more precise control of the amount ofenergy delivered to any particular region of the preform, since theremainder of the preform acts as a heat sink. This makes it possible toshock anneal and/or shock preheat only those regions of the preform inwhich shock annealing and/or shock preheating of the material iscritical for subsequent forming operations, such as cold forming, rollforming, or blow molding. This speeds up the annealing and/or preheatingprocess and reduces overall energy consumption.

In addition, whereas the amount of energy delivered with a stationaryfield can only be controlled by the attributes of the current in thecoil, using a moving field allows for control in several different ways.The speed of heating of a particular region can be controlled by theattributes of the current in the coil and the speed of movement of thefield. Thus, the heating and cooling cycles of selected regions can beshortened by making the field stronger than needed to reach theannealing temperature within a given time, and moving the field tocontrol the amount of time any particular region of the preform isexposed to the field. That allows for a much faster completion of theheating (shock annealing or shock preheating) step. Using a more focusedand/or stronger field at a higher rate of displacement also allows for amore precise definition of the region heated at any given time than witha stationary coil. Thus, by moving the field, a very precise control ofthe heating process is possible. In addition, using a moving field isadvantageous over the simultaneous use of multiple stationary fields,since heating individual regions in parallel has the disadvantage thatthe regions of the preform located between the individually heatedregions are subject to waste heat (due to conduction), which makes itdifficult to precisely control the amount of heat generated at aspecific location of the preform.

In still another aspect, the invention provides a further improvedmethod for fluid pressure molding a metal container from a preformhaving a substantially cylindrical sidewall, an open end and a closedend, for example a preform having been impact extruded from a metalslug. The method includes the selective shock annealing of individualregions of the preform with an electro-magnetic field and subsequentmovement of the same or a different electro-magnetic field relative tothe preform for selectively shock preheating at least a region of thepreform prior to further forming of the preform.

In one embodiment, the electromagnetic field is also variable instrength. This combines the advantages of the movable field with theadvantages of variable inductive heating of individual regions. This isparticularly advantageous for the induction heating (for shock annealingor shock preheating) of regions in the preform which have different wallthickness. Moreover, even if only a single electro-magnetic field isused, a pattern of substantially fully annealed and partially annealedregions (slices) and/or preheated regions (slices) can be created in thepreform by varying the field strength as the field moves axiallyrelative the preform.

In another embodiment, shaped induction coils are used which generate ashaped field. The shaped field is used to generate a shaped pattern ofdifferently heated regions in the preform for shock annealing or shockpreheating. The pattern may be asymmetric.

In still another embodiment, a pattern of differently heated (shockannealed or shock preheated) regions in the preform is generated byusing induction coils inside and/or outside the preform. The pattern maybe asymmetric.

In yet another embodiment, an asymmetric pattern of heating is achievedby moving the electro-magnetic field in more than one axis of thepreform.

In one embodiment, the method further includes the steps of adding acoating on at least one of an interior surface of the preform (lacquer,powder coat, etc.) and an exterior surface of the preform (powder coat,paint, label, sprayed or printed image, adhesive label, flex label,etc.). A label can also be printed onto the exterior surface of thepreform. The method can also include the additional steps of coldworking an upper portion of the preform adjacent the open end to form aneck, and trimming and curling an upper edge of the preform adjacent tothe open end. If a coating is provided on one or more of the interior orexterior surfaces of the preform, shock preheating can be used to heatthe material of the preform to a temperature in excess of the curingtemperature of the coating and even to a temperature in excess of thetemperature at which heat damage to the coating would theoreticallycommence. Moreover, since the coating is in contact with the preheatedpreform material with only one of its surfaces, some cooling of thecoating or label occurs on the surface exposed to ambient conditions, sothat even elevated temperatures on the contact surface which aresomewhat above the temperature at which heat damage will occur will notlead to a complete heating through of the coating, thereby avoiding heatdamage. This is especially the case when a relatively movingelectro-magnetic field is used, since the local temperatures of thepreform can be controlled much more precisely than with a stationaryfield and temporally much shorter heat spikes can be generated. Asdiscussed above in relation to the annealing step, a desired temperaturecan be achieved more quickly and much shorter heating and cooling cyclescan be achieved with a moving electro-magnetic field, which means thetime during which the coating is exposed to the preheat temperature and,thus, potential damage to the coating, can be reduced by using a movingfield. As previously stated, a moving electro-magnetic field can beachieved by moving the field, or the field generating coil, in relationto the coated preform, by moving the preform in the field, or by doingboth.

In a preferred embodiment, shaped induction coils are used whichgenerate a shaped field to generate a pattern of differently preheatedregions in the coated preform. The pattern may be asymmetric.

In still another embodiment, a pattern of differently preheated regionsin the coated preform is generated, by using induction coils insideand/or outside the coated preform. The pattern may be asymmetric.

Shaping Die

The inventors have also discovered that the use of a die made of heatinsulating material can be advantageous, to overcome the heat sinkproblem created by the use of a metal die. The inventors have discoveredthat the high conductivity and heat sink capacity of a metal die can insome cases distort the preheating pattern of a preheated preform, evenwithout contact between the preform and the die. Moreover, when thepreform is pre-heated after insertion into the shaping (blow molding)die, a portion of the preheating energy will be lost to the large heatsink capacity of a metal shaping die, potentially increasing energyconsumption and/or treatment times during preheating. Also, a metal diemay interfere with the induction heating of a preform in the die, forexample by distortion of the electromagnetic field. Thus, the diematerial is advantageously electrically non-conductive.

In another aspect, the invention provides a shaping die for use in amethod of blow molding a metal container, which shaping die has a diecavity defining a shape into which the container is to be molded, and ismainly made of a material with lower thermal conductivity than metal,for example a heat insulating material and/or electrically insulatingmaterial. In one embodiment, the die is made of a hard plastic material,such as a phenolic resin, or other thermoset plastic materials.

Molded Container

The molding process of the present invention enables production of blowmolded containers from an impact extruded preform with cylindricalsidewall having a first (starting) diameter, which shaped containershave an expanded sidewall defining an overall shape of the container andexpanded to a second diameter (expanded diameter) that is 20% to 50%larger than the first diameter, and a three-dimensional relief structurein the expanded sidewall, the three-dimensional relief structureincluding at least one relief feature (protrusion and/or recess)deformed from the expanded sidewall to a relative elevation (height ofprotrusion or depth of recess) of 0.1-10% of the second diameter at thelocation of the relief feature, the relief feature including at leastone edge with a bending radius of 0.3-5 mm.

In one embodiment, the expanded sidewall has a second diameter 20-45%larger than the first diameter.

In another embodiment, the relief feature has a relative elevation of5-10% and the edge has a bending radius of 0.3-3 mm.

In a further embodiment, the blow molded container includes at least onerelief feature in the form of a protrusion directly adjacent at leastone relief feature in the form of a recess.

In still another embodiment, the blow molded container has an overallmolded shape asymmetrical to a longitudinal axis of the container.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be readily understood, an exemplaryembodiment of the invention is illustrated by way of example in theaccompanying drawings.

FIG. 1 is a schematic view of a tooling setup for the shock annealingmethod in accordance with the invention, including a stationary mandreland a movable induction coil;

FIG. 2 shows the tooling setup of FIG. 1 with a preform positioned onthe mandrel and the induction coil moving through a first regionadjacent the closed end of the preform;

FIG. 3 shows the tooling setup of FIG. 1 with a preform positioned onthe mandrel and the induction coil moving through a second regionwithout being fully powered;

FIG. 4 shows the tooling setup of FIG. 1 with a preform positioned onthe mandrel and the induction coil moving through a third region;

FIG. 5 shows the tooling setup of FIG. 1 with a preform positioned onthe mandrel and the induction coil moving through a fourth regionadjacent the open end of the preform;

FIG. 6 is a schematic view of a tooling setup for thepressure-ram-forming process in accordance with the invention;

FIG. 7 is a schematic view of the tooling setup of FIG. 6 with a preforminserted therein;

FIG. 8 is a schematic view of the tooling setup of FIG. 6 with thepreform inserted and prior to preheating, with the induction coilpositioned at the closed end of the preform;

FIG. 9 is a schematic view of the tooling setup of FIG. 6 with thepreform inserted and having been preheated, the induction coil beingpositioned at the open end of the preform;

FIG. 10 is a schematic view of the tooling setup of FIG. 6 with thepreform in the closed mold, prior to filling with pressurized fluid;

FIG. 11 is a schematic view of the molding setup of FIG. 10 with thepreform fully expanded to match the shape of the mold cavity;

FIG. 12 is a side view of a solid aluminum slug in the shape of a discwith one beveled edge, for use in impact extrusion of a metal preform;

FIG. 13 is a partial axial cross-section of an impact extruded preformmade from the slug of FIG. 12 and being a substantially hollow cylinderwith an open end, a side wall and a closed end, as used in the processillustrated schematically in FIGS. 6 to 11;

FIG. 14 is a side view of the preform of FIG. 13 after trimming of theupper edge, annealing, internal/external coating, necking of the upperportion, and curling over of the top edge;

FIG. 15 is a side view of a shaped container in accordance with theinvention, having a sidewall defining a basic, symmetrical overall shapeafter blow molding of the preform has been completed and the upper neckportion has been cold worked to form threads and a bead to receive atamper evident cap closure;

FIG. 16 is a side view of a shaped container in accordance with theinvention, having a sidewall defining a more difficult to achieve,asymmetrical overall shape with three-dimensional relief features;

FIG. 17 is a cross-sectional view of Detail A identified in FIG. 16;

FIG. 18 is a cross-sectional view of Detail B identified in FIG. 16;

FIG. 19 is a cross-sectional view of Detail C identified in FIG. 16; and

FIG. 20 is a cross-section taken along line D-D in FIG. 16.

Further details of the invention and its advantages will be apparentfrom the detailed description included below.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Conventional container forming processes for making a shaped containerfrom a preform made from sheet material, as described, for example, inUS2011/0167886 (incorporated by reference herein in its entirety),generally include the steps of shaping a preform drawing, re-drawing orback extrusion of a sheet material, subjecting the preform material to arecovery anneal, coating and/or labelling of the preform and expandingof the preform to the final desired shape, for example with apressure-ram-forming process.

Impact extruded preforms made by impact extrusion from a metal slug areknown. However, the use of an impact extruded preform in a pressureforming process, for example a ram forming process, although suggestedin US2011/0113732A1 has proven excessively difficult to accomplish.

The inventors have now surprisingly found that the use of an impactextruded preform in a pressure forming process, especially thepressure-ram-forming process in which all expansion of the preform isachieved in a single forming step, can in fact be achieved if thepreform is shock annealed prior to expanding it by pressure forming.Moreover, the inventors have developed a process to differentially shockanneal the preform. An exemplary embodiment of the shock annealingmethod in accordance with the invention, as well as the differentialshock annealing process, will be discussed in more detail below withreference to FIGS. 1 to 5.

The inventors have also discovered that preheating, especiallydifferential preheating, of the preform prior to pressure shaping forpreheating, at least those regions of the preform which will besubjected to elevated expansion during pressure forming, allows for thecreation of a three-dimensional relief structure on the shaped containerpreviously not achievable. An exemplary embodiment of a differentialpreheating process in accordance with the invention will be described inmore detail below with reference to FIGS. 7 to 10.

An exemplary embodiment of a modified PRF process in accordance with theinvention including an inductive preheating of a shock annealed preformprior to pressure expansion will be described in more detail below withreference to FIGS. 6 to 11.

During testing of the modified PRF process in accordance with theinvention, the inventors have further discovered that the use of ashaping die made at least in part of a material having a thermalconductivity lower than that of metal is advantageous for use in themodified PRF process in accordance with the invention. For example ashaping die or shaping mold made of a material which is alsoelectrically non-conductive is advantageous for use when the preform isinductively preheated while suspended in the mold. An exemplaryembodiment of a shaping die or mold in accordance with the inventionwill be described in more detail below with reference to FIG. 6.

The modified PRF process in accordance with the invention enables theproduction of a shaped metal container from an impact extruded preformand with a shape and three-dimensional relief features previously notachievable. Exemplary shaped containers in accordance with the inventionwill be discussed in more detail below with reference to FIGS. 12 to 20.

Shock Annealing

Blow molding of a preform can result in regions of significant materialdeformation and/or expansion. In order to avoid material failure inthose regions, annealing of the preform to increase the ductility isused. The inventors have observed that although conventional type fullannealing of the preform by convection heating, in an oven or the like,increases the ductility of the preform, convection heating has severaldisadvantages. Convective heating is associated with low energyefficiency due to heat losses to the environment and the need forheating not only the preform material, but the space surrounding it.Heating of the preform may also be uneven, leading to uneven annealingof the preform. The same problem can occur with preforms havingvariations in wall thickness. Moreover, although increasing theannealing temperature and/or dwell time will result in more evenannealing of the preform, other, potentially even more serious problemsmay occur.

Theoretically, the higher the annealing temperature and/or the longerthe dwell time, the more complete and even the anneal of the preformmaterial. However, the closer the annealing temperature used is to themelting temperature, the higher the risk of deformation of the preformdue to softening of the preform material. In addition, even at annealingtemperatures that do not necessarily cause deformation of the preform,extended dwell times can lead to warping of the preform and/or graingrowth in the crystalline structure of the preform material leading to aloss in material strength. Deformed or warped preforms or preforms withreduced material strength are undesirable for use in the subsequentshaping of the preform, especially in blow molding.

The inventors have now discovered an advantageous annealing process thatallows the use of significantly higher annealing temperatures thanconventionally used, without the deleterious effects of deforming andwarping. The inventors have also discovered that more aggressive shapingof the preform is made possible with this process than with conventionalfull annealing methods. The annealing method of the invention is basedon shock heating of the preform material to reach the desired annealingtemperature in a very short amount of time, within seconds, while at thesame time the desired annealing temperature is higher thanconventionally used. This annealing method, referred to throughout thisapplication as shock annealing, requires the heating of the preformmaterial to achieve a temperature rise in the preform material of atleast 120° C./sec, advantageously at least 150° C./sec, for example atleast 200° C./sec, for example 235° C./sec until the desired annealingtemperature is reached. Using such a rapid rise in temperature, allowsthe use of annealing temperatures in the range of 65-98%, for exampleabout 90% of the melting point temperature of the material withoutundesired deformation or warping of the preform, since the annealingtemperature is reached within a very short period of time.

Without intending to be bound by this theory, it would appear that themost critical factor for achieving substantially full annealing andmaximum ductility is the maximum annealing temperature reached duringthe process. Moreover, by shock annealing the material for a very shortperiod of time, full realignment of the grains in the crystallinestructure of the preform material appears to be achieved with minimumgrain growth, thereby minimizing the loss of material strength resultingfrom grain growth. In another theory, the degree of anneal is dependenton the total amount of energy transferred into the preform material andusing a high energy flow for a short period of time, as in shockannealing enables the transfer of the total amount of energy requiredfor a substantially full anneal over a significantly short dwell time tominimize material deformation or warping and grain growth. Thus, theadvantages of shock annealing are that the elevated ductility values andminimum loss in material strength are achieved for the preform materialby a simple short-time high-temperature annealing. In addition, theso-called shock annealing causes little or no component deformation orwarping of the article, reducing the rejection percentage and obviatingany process for straightening the preform. In addition, the shockannealing treatment can be most economically achieved by inductionheating of the metal preform.

The inventors have also found that the total amount of energy and theenergy density required for achievement of the desired temperature riseand the final shock annealing temperature is dependent on the mass ofthe preform as well as the efficiency of the induction heating process.The process efficiency in turn is dependent on the ratio between theresistance of the coil and the resistance of the preform as well as thefrequency of the current used to generate the electro-magnetic field.The higher the can resistance, the higher the efficiency. The frequencyused influences the penetration depth of the electro-magnetic field intothe preform material.

In theory, lower frequencies provide for deeper penetration into thematerial and the higher the frequency the lower the efficiency. Thus, itwould be theoretically preferable to use the lowest frequency possibleto achieve the highest efficiency and therefore steepest temperaturerise. However, the temperature rise achieved at any given location inthe preform also depends on the thickness of the preform material atthat location and variations in material thickness can lead to localizedtemperature variations. Those variations are expected to become morepronounced the higher the energy density used, and the higher theefficiency of the process, and can become amplified into uncontrollabletemperature spikes leading to localized burning or melting of thepreform material.

To test the effects of frequency and wall thickness, preforms ofdifferent wall thickness were exposed to an electro-magnetic field ofconstant energy density but variable frequency. The observedcorrelations between frequency, penetration depth and efficiency, areapparent from the results represented in the following table:

TABLE 1 Efficiency % F Penetration 0.011″ 0.013″ 0.015″ 0.020″ (kHz)Depth (in) wall wall wall wall 300 0.0115 38.7% 38.6% 38.7% 38.7% 2000.0141 38.5% 38.5% 38.5% 38.6% 100 0.0200 42.0% 41.0% 40.0% 38.3% 500.0282 53.0% 49.2% 46.0% 38.0%

As is apparent from the results listed, wall thickness, frequency andefficiency were correlated as theoretically expected while thepenetration depth exceeded the wall thickness. However, the impact ofwall thickness on the efficiency became much reduced at 100 kHz andvirtually disappeared at 200 kHz. That means the danger of localizedtemperature spikes due to material thickness tolerances, which spikesare exaggerated at higher energy densities, can be significantly reducedby using higher frequencies than those theoretically practical.Frequencies of 10 kHz to 600 kHz can be used in the process of theinvention, as long as a careful balance is struck between power input(power density) and frequency to minimize the risk of localized burningor melting in a preform of given mass, resistance and wall thickness.However, due to the reduced effect of wall thickness on the heatingprocess efficiency at higher frequencies, a frequency range of 100 kHzto 400 kHz was found practical. Moreover, material density and thicknesstolerances are higher in an impact extruded preform than in a preformdrawn from sheet material and the frequencies found advantageous forimpact extruded preforms are higher than those for drawn preforms. Afrequency range of 200 kHz to 300 kHz was found practical with impactextruded preforms. A frequency of 300 kHz was found most practical forimpact extruded preforms of 0.013″ to 0.018″ (0.330 mm-0.457 mm) wallthickness.

The strains on the material of a metal preform during necking and/orpressure forming may exceed the formability of the work hardenedpreform, especially when an impact extruded preform is used, which has ahigh dislocation density. Pressure forming of an impact extruded preformwill generally lead to material failure upon expansion past 3% of thefirst diameter of the preform (initial or starting diameter). Therefore,for improved formability and expandability, the metal preform in oneembodiment in accordance with the invention is subjected to shockannealing after impact extrusion and prior to any further forming steps.

Annealing of the work hardened preform makes the preform more ductile.The inventors have found that conventional annealing methods heating thepreform in an oven or partially annealing the preform by inductiveheating are unsatisfactory for the achievement of elevated expandabilityand deformability of the preform material in an impact extruded preform.The inventors have further found that shock annealing of the preformprior to any shaping or expansion will maximize the expandability anddeformability of the preform. Shock annealing is defined in thisdescription as heating the material to be annealed to achieve atemperature rise in the material of at least 120° C./sec, to reach anannealing temperature in the range of 65%-98% of the melting pointtemperature of the metal. A temperature rise of at least 150° C./sec wasfound advantageous, for example at least 200° C./sec, or 235° C./sec,and at most 250° C./sec. After sufficient heating time to reach thepreselected final annealing temperature, the heating is stopped and thematerial is allowed to cool. The inventors have found that shockannealing is most advantageously achieved by using inductive heatingwith a power input in the range of 10 kW to 20 kW and a power density of25-100 W/cm² of preform material, for treatment times (dwell times) inthe range of 0.3 to about 4 sec. Moreover, the penetration depth of theinductive field into the material to be annealed and the efficiency ofthe inductive heating process may be controlled by the frequency of theinductive current used to generate the inductive field. The inventorshave found that lower frequencies provide deeper penetration and higherefficiency, while higher frequencies provide more shallow penetrationand lower efficiency. Frequencies in the range of 10 kHz to 600 kHz canbe used with frequencies in the range of 200 kHz to 400 kHz beingadvantageous and a frequency of 300 kHz having been found to provide anadvantageous compromise of penetration depth and efficiency.

Shock annealing can also be used for the annealing of preforms made fromsheet material. Table 2 below illustrates the expected effect of partialor full annealing using conventional methods as disclosed in U.S. Pat.Nos. 5,058,408, 6,349,586 and 5,776,270 on the expandability of apreform, as compared to shock annealing in accordance with theinvention. The results expected upon a 20% PRF expansion of preformsannealed with the prior art methods are compared to those achieved withan impact extruded aluminum preform (38 mm diameter) shock annealed andexpanded in a PRF setup by at least 25% in accordance with theinvention. Power input was calculated on the basis of total power inputand coil diameter. Material failure means the presence ofmicro-perforations, visible perforations or stress cracking at a bendingradius in the expanded region of the sidewall of 5 mm or less.

TABLE 2 Annealing Dwell Power Annealing Temperature time in input Cansize Material Method range seconds W/in² OD mm Failure U.S. Pat. No.450-650° F. 2 1020 63.50 yes 5,058,408 232-343° C. U.S. Pat. No.450-700° F. 2 943 66 yes 5,776,270 232-371° C. U.S. Pat. No. 450-650° F.2 1100 63.5 yes 6,349,586 232-343° C. Shock 840-1100° F.  2 8824 38 noanneal 450-600° C.

The inventors have further surprisingly discovered that despite thesignificant dislocation density in the material of an impact extrudedpreform, an impact extruded preform including differentially shockannealed regions, wherein not all regions of the preform aresubstantially fully annealed, can be successfully used for forming withthe PRF process. The term differentially shock annealed portions as usedin this disclosure defines adjacent regions in the preform which differin degree of annealing, whereby the degree of annealing can range frompartial annealing to substantially full annealing, as long as thoseregions subject to the largest expansion or deformation during thedownstream pressure forming process have been substantially fullyannealed. The inventors have found that substantially fully shockannealing only those regions of the preform which are subject toelevated strain during molding is sufficient, as long as the remainingregions of the preform are at least 70% annealed, since some regions ofthe preform, such as those at the closed bottom end, can be produced atapproximately the final shaped size. This may speed up the formingprocess and reduce power consumption. Choosing a final shape thatreduces the amount of material that is stretched during pressure formingalso reduces the regions of the preform that require a higher ductilityand hence require full shock annealing. The energy costs andmanufacturing cycle times may be even further reduced by using a movableelectro-magnetic field for induction heating.

In the exemplary embodiment, the preform is annealed by generating anelectro-magnetic field of an energy density of about 25 W/cm² to about100 W/cm² of the preform material, advantageously about 40 W/cm² toabout 90 W/cm², for example 86 W/cm², for inducing a current in thepreform and selectively exposing a first region of the preform to theelectro-magnetic field for sufficient time to achieve a shock annealingof the first region, and thereafter selectively exposing the remainingregions of the preform to the same electro-magnetic field for the samedwell time to shock anneal the entire preform to a substantially fullanneal. It is also possible to use fields of differing energy densityfor different regions of the preform, or to use the same energy densityfor all regions, but to vary the dwell time to achieve shock annealingof the different sections for a 70-100% anneal. The individual regionsof the preform can be sequentially exposed using a single inductioncoil, or simultaneously exposed using a segmented coil. If a single coilis used, relative movement between the electro-magnetic field and thepreform is achieved by either moving the coil relative to the preform,or moving the preform relative to the coil, or both.

An exemplary setup for selectively exposing one or more regions of thepreform to the electro-magnetic field is illustrated in FIG. 1. Thesetup includes a base 60, a mandrel 62 mounted to the base, for examplein a vertically upright position, an induction heater mount 64 and aninduction heater 66, including an induction coil 70. The inductionheater 66 with coil 70 is mounted to the mount 64 so that coil 70 iscoaxial with mandrel 62 and movable between a loading position A at thetop of mount 64 to a fully lowered position B (illustrated in brokenlines).

The sequential exposure of different regions of the preform will bediscussed in the following with reference to FIGS. 2 to 5. FIG. 2 showsa preform 18 placed on the mandrel 62 with the closed end 20 resting ona dome shaped top end 63 (see FIG. 1) of the mandrel 62 and the open end22 oriented downward so that gravity holds the preform on the mandrel.Arrangements in which the mandrel and induction heater mount areoriented other than vertical and the preform is held on the mandrel bymeans other than gravity, for example by a vacuum pressure, can also beused. The terms upper end, open end and upper open end areinterchangeably used throughout this specification and all define theopen end of the preform, while the terms bottom end, closed end andclosed bottom end are interchangeably used throughout this specificationand define the closed end of the preform.

In the exemplary process discussed and solely for ease of reference, thepreform is divided into axially transverse sections (regions) A-C, C-D,D-E, E-F and F-B. Those sections may represent the closed end of thepreform (A-C) a bottom end of the sidewall adjacent the base (C-D), alower midsection of the sidewall (D-E), an upper midsection of thesidewall (E-F) and a neck of the preform (F-B). By moving the inductionheater 66 from position A to position B, each section of the preform canbe induction heated individually and in sequence with the respectivelyadjacent portions. In the illustrated example, the lower end of thesidewall is annealed by movement of fully energized coil 70 over sectionC-D (FIG. 2), the lower midsection of the sidewall is heated less bymoving the coil 70, partially energized (as illustrated by the brokenlines), over section D-E (FIG. 3), the upper midsection is annealed bymovement of fully energized coil 70 over section E-F (FIG. 4) and theneck of the preform is minimally annealed by moving the lightlyenergized coil 70 quickly over the section F-B (FIG. 5), or not annealedat all. The annealing temperature achieved in each section will dependon the size and frequency of the current flowing through coil 70, thesize, diameter and number of windings of the coil 70, the spacing of thecoil 70 from the preform, the resistance ratio between the coil and thepreform, and the rate of advancement of the induction heater 66 in eachsection. All of these structural features of the coil 70 have an effecton the energy density in the field generated by the coil. In theillustrated example, a coil capable of generating a field with an energydensity of 25-100 W/cm², for example about 86 W/cm², was used. The powerinput to the coil was 10-20 kW, for example 15 kW. The spacing of thecoil 70 from the preform 18, the size of the coil and the number ofwindings all influence the field density and are generally fixed.However, each of the remaining parameters can be controlledindependently to control the final annealing temperature achieved in theregion of the preform within each section and to control the speed ofthe temperature increase in each region. Accordingly, each region can beheated at a separate temperature. For example, if the neck portion ofthe preform is to be significantly compressed during necking, it may bedesirable to substantially fully anneal the neck portion and heat thewhole neck portion to an annealing temperature of 525° C.

The induction heater may include at least one induction coil 70, such asa solenoid coil, for inducing an electromagnetic field in the preform18. The induction coil can include multiple coil members (not shown) ora continuous coil member with multiple windings, as schematicallyillustrated in FIGS. 1 to 5. The induction coil may be a hollow tube toallow for cooling of the coil when higher currents are applied. In theexemplary embodiment, the induction coil is formed of ¼ inch squarecopper tubing and the inner diameter of the coil is adjusted to create aminimum spacing of 1 mm from the preform at all times. Suitableinduction coils are commercially available (Fairview Coil Fabrication(FCF), Scottsville, N.Y.). In general, the coil is shaped and sized togenerate the electromagnetic field uniformly throughout the region ofthe preform in which the inductive current is induced.

The induction coil can be electrically connected to a power source byvarious devices including conductive wire or conductive tubularconnections. The tubular connections can be formed by extensions of thecopper tubing that forms the induction coil. In the exemplaryembodiment, the power source provides an electrical current, forexample, an alternating current of about 380V at 300 kHz. The current isconducted through the induction coil and induces an electromagneticfield within the preform. The annealing temperature reached in thepreform can be determined by monitoring the power supplied by the powersource. The penetration depth and efficiency of the inductive field inthe material to be annealed can be controlled by the frequency of theinductive current. Lower frequencies provide deeper penetration athigher efficiency, while higher frequencies provide lower efficiency atmore shallow penetration. Frequencies in the range of 10 kHz to 600 kHzcan be used with frequencies in the range of 200 kHz to 400 kHz beingadvantageous. In the exemplary embodiment, a frequency of 300 kHz, wasused, providing a good compromise of penetration depth and efficiency.

When the induction coil winding is tubular and defines a passage forcirculating a cooling fluid, the coil can be connected by one or morehoses, pipes, tubes, or other conduits to a coolant source. A pump canbe provided for circulating the cooling fluid from the coolant sourcethrough the induction coil and back. This allows the use of highercurrents inducing fields with higher energy densities, since overheatingof the coil can be prevented by circulating a cooling fluid through thecoil.

Molding Process

U.S. Pat. No. 7,107,804 (incorporated by reference herein in itsentirety) discloses the pressure-ram-forming process (PRF) wherein ametal container of defined shape and lateral dimensions is formed bothby fluid pressure, applied either internally or internally andexternally, and by the translation of a ram driven by a shaft. In themethod disclosed, a hollow metal preform formed by a draw, re-draw orback extrusion process from a metal sheet and having a closed end, isplaced in a die cavity laterally enclosed by a die wall defining theshape and lateral dimensions of the finished container. A ram located atone end of the die cavity is translatable into the cavity. The preformis positioned in the die with the closed end being positioned inproximate facing relation to the ram. The preform is initially spacedinwardly from the die wall, but upon being subjected to the fluidpressure expands outwardly into substantially full contact with the diewall. This imparts the defined shape and lateral dimensions to thepreform. After the preform begins to expand but before expansion of thepreform is complete, the ram is translated into the cavity to engage anddisplace the closed end of the preform in a direction opposite to thedirection of force exerted by fluid pressure and to deform the closedend of the preform inward. The defined shape, in which the container isformed, may be a bottle shape including a neck portion and a bodyportion larger in lateral dimensions than the neck portion. The die isgenerally a split die, which is separable for removal of the formedcontainer and allows for a defined shape that may be asymmetric aboutthe long axis of the cavity.

Necking of the preform may occur in the pressure forming step, at anytime after annealing and prior to pressure forming, or after pressureforming. There are several options for the complete forming path and theappropriate choice is determined by the formability of the metal sheetor slug being used. The preform can be made from aluminum sheet with agauge in the range of 0.25 mm to 1.5 mm or from a disc shaped slug 30 ofmetal as shown in FIG. 12, which is formed by saw cutting the disc fromround bar stock or by a smelting process and annealed and surfacetreated. The preform is a closed-end cylinder that can be made fromsheet material by, for example, a draw-redraw (-redraw) process, byback-extrusion, or from a slug by impact extrusion. The diameter of thepreform generally lies somewhere between the minimum and maximumdiameters of the desired container product, although slightly largerpreform diameters can be used, as long as wrinkling or folding of thepreform upon closure of the shaping die is avoided.

The preform may be an aluminum preform. The method of the inventioncould also be used to shape containers from other materials, such assteel, tin, lead, copper, or magnesium, or alloys thereof. Although itwill be appreciated by the person skilled in the art that the targetannealing temperatures discussed herein in relation to the shockannealing of an aluminum preform will have to be adjusted for the shockannealing of other metals, the principal concept of shock annealing byachieving a temperature rise of at least 120° C./sec is applicable toother types of metal preforms, taking into consideration the specificproperties and behaviour of the respective material upon inductionheating. For example, steel is magnetic and has higher electricalresistivity and could therefore be heated faster. However, for the samereasons steel heats faster at the surface than deeper inside the sidewall. Thus, skin effects may occur in steel preforms with relativelythick sidewalls. These effects are however known and a person with skillin the art would be able to properly select the conditions to executethe shock annealing method of the present invention with preforms ofdifferent materials.

An impact extruded preform is shown in FIG. 2. An aluminum slug 30 of 12mm thickness, 38 mm diameter (first diameter) and generally selectedfrom a 1000 or 3000 series Alloy was used to create the preform. Theslug is impact extruded in a conventional manner between an annular dieand a cylindrical punch (not shown) to produce a hollow preform 18having a substantially cylindrical side wall 19, an upper open end 22and an outwardly concave, flat, or outwardly convex lower closed end 20.The impact extrusion process leaves an irregular upper edge. Trimming anupper portion of the edge of the preform adjacent the upper open endproduces a square top edge. After trimming, and brushing if required,the preform is cleaned of lubricant or cutting oil, for example with acaustic wash. Conventional trimming, brushing and cleaning processes canbe used.

Shaped containers for use in food packaging may require an interiorcoating or lacquer to prevent corrosion and spoiling of the contents, orfor sanitary reasons. The exterior of the container generally alsorequires a coating for durability, labeling, decorative appearance andmarketing reasons. The interior and/or exterior coatings are generallyapplied prior to pressure forming, since their application of after blowmolding onto the shaped container of complex shape is difficult moredifficult than simply applying them to the preform of simple cylindricalshape. However excessive strain or stretching of the preform materialduring blow molding can damage those coatings, as can preheating of thepreform prior to molding.

A necked preform is shown in FIG. 14, which is obtained by cold workingof the upper portion of the preform adjacent the open end to form a neck23. Various conventional shaping operations can be used for necking of apreform. The preform is generally subjected to a series of dies thatdraw the preform material gradually into the finished shoulder shape.This process is well known to the person of skill in the art and neednot be discussed in more detail herein. The spout can be roll formed ina conventional manner into a collar 24. Trimming, necking and curlingthe upper end of the preform adjacent to the open end produces thepartially finished upper portion of the preform seen in FIG. 14.

One or more surface coatings are preferably applied after annealing andprior to pressure forming and cured on the interior surface of thepreform and/or on the exterior surface of the preform. The type ofcoating may include any type of known coating for containers of thistype, such as a base or primer coating, a printed coating with productlabeling, powder coatings, lacquers, clear protective over-varnishcoatings, adhesive labels, flex labels, etc.

As schematically illustrated in FIGS. 5 to 11, the pressure-ram-formingprocess uses a basic tooling setup including a split die 10 with aprofiled cavity 11 defining a bottle shape, a ram 12 that has thecontour desired for the bottom of the container (for example a convexlydomed contour 12 a for imparting a concavely domed shape to the bottomof the formed container) and a shaft 14 that is attached to the ram. Forease of manufacturing, the die is preferably oriented with the bottleshape being axially vertical. Sealing of the preform in the die is aidedby orienting the preform upside down. The die is equally oriented withthe bottle shape upside down. The two halves of the split die may bemirror image for the production of a symmetrical bottle as shown in FIG.15, or different (as shown in FIGS. 5-11) for the production of anasymmetrical bottle as shown in FIG. 16. During pressure forming, thetwo die halves 10 a, 10 b are pressed together and match in a planecontaining the longitudinal axis of the bottle shape defined by the diecavity 11. If preheating of the preform prior to pressure forming isdesired, a coil 50 is included in the basic tooling setup, which can bemoved axially over the preform 18. Advantageously, the coil 50 isconstructed and mounted in such a way that is can be moved along thepreform 18 while the preform is suspended in the open die 10 as will bedescribed in the following. An alternate embodiment in which the coil 50is constructed and mounted in such a manner to move coaxially with thepreform on the outside of the closed die 10 is also possible.

As illustrated in FIG. 6, the preform is positioned in the die cavity 11below the ram 12 and has a schematically represented pressure fitting 16at the open end 11 a to allow for internal pressurization. At the openend 11 a, the minimum diameter of the die cavity 11 is equal to theoutside diameter of the preform 18. Pressurization can also be achievedby some other type of pressure fitting.

The fluid pressure forming step involves closing the die or mold 11around the preform 18 as illustrated in FIG. 9 and introducing, into theinterior of the hollow preform 18, a fluid under such pressure as tocause the preform 18 to expand outward towards the wall of the diecavity 11. Expansion of the preform 18 continues until the wall of thepreform is snug against the die wall as shown in FIG. 10. This matchesthe shape and lateral dimensions of the expanded preform 18 to those ofthe cavity 11, so that the preform takes on the desired shape.

Compressible or non-compressible fluids can be used for pressurizationof the preform. If liquids are used, care must be taken to limit theforming operations to temperatures below the boiling point of theliquid. Once the desired shape is achieved, the pressurizing fluidpressure is released, the split die is opened and the formed containeras shown in FIG. 4a or 4 b (depending on the shape of the die used) isremoved from the die.

In the illustrated exemplary embodiment, the preform 18 is a hollowcylindrical aluminum workpiece with a closed lower end 20 and an openupper end 22, having an outside diameter equal to the outside diameterof the neck of the bottle shape to be formed. The motion of the shaft 14and the rate of internal pressurization are such as to minimize thestrains of the forming operation and to produce the desired shape of thecontainer. Neck and side-wall features result primarily from theexpansion of the preform due to internal pressure, while the shape ofthe bottom is defined primarily by the motion of the shaft and ram 12,and the contour of the ram surface facing the preform closed end 20.

The synchronization of the preform pressurization with the advance ofthe shaft and ram limits axial stretching of the preform under theinfluence of the supplied internal pressure. While the preform is beingexpanded, its axial length decreases. By advancing the ram duringexpansion of the preform, detachment of the closed end of the preformfrom the side wall is prevented. Moreover, as the preform approaches thefinal, expanded shape, advancement of the shaft 14 continues to forcethe ram against the closed end of the preform to deform the closed endof the preform upwardly until it matches the shape of the ram.

Prior to blow molding, the preform can be preheated either in the moldin the loading position (as shown in FIGS. 7 and 8) or outside the moldin an exterior induction heater (not shown).

Preheating

Preheating of the preform can be achieved with heaters within the mold,exterior heaters, or induction heaters exterior or interior to thepreform. In one embodiment of the shaping process in accordance with theinvention, an aluminum alloy preform 18 with a coating is used, which ispreheated to a temperature of less than or equal to 200° C., in order tominimize damage to the coating, while providing greater ductility forblow molding.

In a second embodiment, the process includes preheating a selectedregion of the side wall of the preform by heating to a preheatingtemperature with an induction coil 50. The induction coil 50, and forexample the electro-magnetic field generated by the induction coil andthe currents in the preform induced by the field, heat the material morequickly and with less energy than, for example, a radiant heater.Further, an induction heater can be directed to heat only the selectedregions while maintaining the remaining regions of the side wall andremaining regions of the closed end below the preheating temperature. Atemperature gradient between the preheated and the remaining regionswill naturally occur due to the thermal conductivity of the aluminummaterial of the preform. The preheating step can also be performed witha first induction heater disposed externally to the preform and a secondinduction heater disposed internally to the preform. The small size ofinduction heaters enables access to the interior of the containerpreform. Induction heating also exposes any coatings to heat for ashorter period of time thereby reducing the potential for heat damage tothe coating during the pressure forming. Induction heaters of theprincipal construction discussed above in relation to the annealing stepcan be used for the preheating step.

In the second embodiment of the preheating step in accordance with theinvention, shock preheating of the preform 18 can be used in which thecoated preform is subjected to inductive heating to achieve atemperature rise in the preform of at least 120° C./sec. When shockpreheating is used, the preform material can be heated to a preheatingtemperature in the range of 100 to 300° C. for a treatment time of lessthan 4 sec. In another embodiment, the preform can be shock preheated toa preheating temperature in the range of 100 to 200° C. for a treatmenttime of 0.1 to 2 sec. Conventional coatings applied to food gradecontainers have a temperature tolerance limit, above which heat damageto the coating occurs, generally in the range of 100 to 200° C. Thus,preheating of the preform during blow molding is generally limited to atemperature below the temperature tolerance limit of the coating.However, when shock preheating is used, the preform material can beheated to a temperature up to 50% above the tolerance limit, which isvery advantageous for the pressure shaping step, since the higher thepreheating temperature, the more ductile the preform material, the moreexpansion the material will withstand prior to material failure. Despitethe temperature being in excess of the temperature tolerance limit,damage to the coating is minimal or avoided by the generally shorttreatment time and the generally low heat conductivity of the coating aswell as the cooling of the coating by contact with the surrounding air,which is usually at or near ambient temperature. In this exemplaryembodiment of the process of the invention, a treatment time of lessthan 2 seconds was selected. The energy density of the electro-magneticfield used for shock preheating in the exemplary process was selected asdescribed above in relation to the shock annealing process.

In the second embodiment of the preheating of the preform in accordancewith the invention, the preform 18 is preheated while positioned withinthe opened die 10 and before enclosure of the preform within the diecavity 11, as will be discussed in the following with reference to FIGS.7 and 8. In the exemplary process, the preform 18 is preheated bygenerating an electro-magnetic field with coil 50 for inducing a currentin the preform 18 and selectively exposing first and second regions 18a, 18 b of the preform to the electro-magnetic field for inductionheating of the first and second regions each to an annealingtemperature. The first and second regions 18 a, 18 b are preferablyexposed by moving the electro-magnetic field relative to the preform 18.This is achieved either by moving the preform through the field, bymoving the field, as illustrated in FIGS. 7 and 8, wherein the coil 50generating the field is moved over the preform 18, or within the preform(not illustrated), or by doing both, moving the preform and the field(not illustrated). In one embodiment, the first and second regions arefirst and second transverse sections of the preform 18.

To progress from the preform shape of FIG. 3 to the fully molded can 40,40 a in the shape shown in FIGS. 15 and 16 respectively, the die or mold10 is closed to surround the preform and the upper open end of thepreform is sealed as shown in FIG. 9. The preform is filled withpressurized fluid (gas or liquid) and, as noted above, the ram 12 movesfrom the loading position 52 shown in FIGS. 6, 8 and 9, wherein only acentering point 12 b on the convex portion 12 a of the ram 12 (FIGS.5-7) engages the closed end 20 of the preform (FIG. 7), to the moldedposition 54, wherein the whole convex portion 12 a of the ram 12 engagesthe closed end 20 of the preform 18 (see FIG. 10) and forms the closedend into a concave bottom for the finished container 40 a, 40 b.

A shaping pressure of 60 bar or less was used in the exemplary processand any pressures above 20 bar have been found to be adequate. Thecombined interior pressure and movement of the mold base expand theselected and annealed regions of the side wall of the preform radiallyoutwardly to engage the interior side surface of the mold. The preformclosed end is also formed from an outwardly concave, flat or convexshape to an outwardly concave shape matching the mold base.

The contact force between the closed end of the preform and thecentering point 12 b on the ram 12, which contact force is generated bythe shaping pressure on the interior surface of the preform closed endis generally sufficient to restrain the closed end in the die againstlateral movement during expansion of the preform. However, in someinstances, the fluid pressure inside the preform can be inadequate tocreate a sufficient contact force to prevent lateral movement of thepreform closed end. For those situations, the preform can be providedwith an alignment dimple in an exterior surface of the closed end forengagement by a matching alignment protrusion on the ram 12 for examplethe centering point 12.

Molded Container

The shaping process of the present invention enables the manufacture ofshaped metal container in accordance with the invention, which ispressure molded in one expansion step from an impact extruded aluminumpreform having a cylindrical sidewall of a first diameter (initial orstarting diameter) and a closed bottom end. The shaped metal containerincludes a closed end (bottom end), for example an inwardly domed bottomend, and a sidewall defining an overall shape of the container. In atleast one shaped region, the shaped container has an expanded diameter(second diameter) larger than the first diameter. The sidewall, in theat least one shaped region, further includes a three-dimensional reliefstructure. The three dimensional relief structure includes at least onerelief feature deformed from the sidewall to a relative elevation of0.1-10% of the second diameter at the location of the relief feature andthe relief feature includes at least one edge with a bending radius of0.3-5 mm. The maximum overall expansion of the sidewall at the relieffeature is 25% to 50% of the first diameter. An exemplary shapedcontainer with symmetrical shape is shown in FIG. 15, while a shapedcontainer with asymmetrical shape and multiple three-dimensional relieffeatures of variable appearance is shown in FIG. 16. Detail views ofcertain relief features of the container of FIG. 16 are illustrated inFIGS. 17-20, in which the bending radius at the respective bends and oredges of the relief structure are identified as Rx, whereby R stands forradius and x identifies the size of the respective radius in mm.

By using the shock annealing process in accordance with the inventionand, as needed, also the shock preheating process of the invention,shaped metal containers can be manufactured from metal preforms, whichcontainers have a surface relief structure previously not attainable.Using the shock annealing and shock preheating processes in combination,shaped metal containers can be obtained wherein the container sidewallhas been subjected in a single expansion step to a maximum overallexpansion of 25-45% of the first diameter. The shaped metal containersin accordance with the invention can have one or more relief features ofa relative elevation of 5-10% and one or more edges with a bendingradius of 0.3-3 mm. The relief features can be a protrusion from thesidewall, or a recess in the sidewall. Shaped containers in whichprotrusions and recesses are directly adjacent can also be produced. Theoverall shape of the container can be symmetrical to a longitudinal axisof the container or asymmetrical to the longitudinal axis. As shown inFIG. 15, after blow molding is completed and the container is removedfrom the mold, threads can be formed on an upper portion of the neck anda curled over bead can be formed on the upper edge of the neck.

Shaping Die

The shaping mold or shaping die 10 used in the exemplary process inaccordance with the invention as schematically illustrated in FIGS. 6 to11 can be formed of any material able to withstand a forming pressure upto at least 60 bar. In one embodiment, the shaping die 10 for use in thepressure forming of metal containers of a predeterminedthree-dimensional shape, includes a mold body having an interior surfacecomplementary to the predetermined three-dimensional shape. A majorityof the body is advantageously made from a material having a thermalconductivity lower than metal. In one embodiment, the majority of thebody is made of a heat insulating material. In another embodiment, thematerial of the body is also electrically non-conductive, for example aplastic material selected from the group of phenolic resins, or otherthermoset resins. One exemplary die 10 used in the process of theinvention was cast from a phenolic resin-cotton fabric material. Otherpossible materials are melamine resins, epoxy resins, epoxy resinsreinforced with paper substrates, fiberglass substrates or syntheticsubstrates (combination phenolilc, epoxy, Kevlar, carbon fiber, etc. . .. ). Another exemplary die was provided on the interior surface of themold with a metal coating applied by metal vapour deposition, forincreasing a wear resistance of the interior surface and for providingcooling of the expanded preform upon contact with the die.

EXAMPLE

Preform

Commercially available aluminum slugs made of a Series 1100 or 3000Alloy, having a 38 mm diameter and 12 mm thickness were impact extrudedin a conventional impact extruder setup (Schuler Press) into ancylindrical aluminum preform of 38 mm diameter having a closed, flatbottom and a cylindrical sidewall of about 200 mm height and 0.333 mmthickness. The preform was subjected to conventional trimming, cleaningand brushing treatments, to generate an even top edge, remove extrusionlubricant and provide an overall even external appearance.

Annealing

A commercially available cylindrical induction coil (FCF) of 42 mmdiameter and about 50 mm height was used in the annealing treatment. Thepreform was placed on the mandrel 63 and the coil 70 was moved over thepreform at constant speed. A voltage of 380V at a frequency of 300 Hzwas applied to the coil at a total energy input of 15 kW. The efficiencyof the induction heating process was calculated at about 38%, whichtranslated into a total energy input into the surface area of thepreform under the coil of 5.2 kW. At a coil height of 50.8 mm and OD ofthe can of 38 mm the surface area of the preform under the coil is 85.79cm² and thus the power density input into the preform was about 85.8W/cm². The speed of advancement of the coil was selected to expose eachaxial location on the preform for about 2 seconds to theelectro-magnetic field generated by the coil. The final annealingtemperature reached was 510° C., translating into a temperature rise ofabout 240° C./sec, at an ambient temperature of about 26° C. Each axialregion of the preform was exposed to the electro-magnetic field andthereby heated only for the time required for the coil to pass over theregion. Cooling of the region by ambient conditions commencedimmediately after passage of the coil. After a complete pass axiallyalong the whole preform, the coil was returned to the starting location.

Coating and Necking

After cooling to a temperature below 100° C., the preform was providedwith an interior lacquer coating and an exterior printed label, usingconventional technologies. The coated and decorated preform was thensubjected to a conventional necking procedure to generate a rimmed neckas illustrated in FIG. 14.

Preheating

Preheating of the preform can be carried out outside or inside the die.When preheated external to the die, the preform is preheated in anintermediate position in order to reduce cycle time and improve machineefficiency. Although external heating could be performed more easily,more cooling of the preform can occur prior to shaping than withpreheating inside the die. In this example, the coated and decoratedpreform was moved into the opened die 10 as illustrated in FIG. 7, andpreheated by exposure to a moving electro-magnetic field. A coil of thesame dimensions as described above in relation to the annealing step wasused. The energy input into the preform was controlled for the preformmaterial to reach a temperature of 300° C. and to limit the exposuretime of any part of the preform material to at most 2 seconds. Theenergy density supplied into the preform material was of 40 W/cm² andthe temperature rise was at most 140° C./sec. In other words, thepreform was exposed to a shock preheating process similar to the shockannealing process described above in relation to the annealing step.Differential preheating was achieved by modifying both field strengthand coil advancement speed as the coil was moved axially along thepreform. After a complete pass axially along the whole preform, the coilwas returned to the starting location.

Shaping

The die 10 was closed as shown in FIG. 10, pressurized with compressedair to about 50 bar to force the preform sidewall 18 against the diecavity 11 and the ram 12 was moved into the die to form a concave bottomend on the container. After completion of the shaping process, the die10 was opened and the shaped container, as illustrated in FIG. 16, wasremoved from the die.

Although the above description relates to specific preferred embodimentsas presently contemplated by the inventors, it will be understood thatthe invention in its broad aspect includes mechanical and functionalequivalents of the elements described herein.

What is claimed is:
 1. A method of pressure molding a shaped metalcontainer of a desired shape from a metal preform having a cylindricalbody with an open end and a closed end, the method comprising:generating an electro-magnetic field; and shock annealing at least oneregion of an aluminum or aluminum alloy preform by exposing the preformto the electro-magnetic field for inductively heating material of thepreform to generate a temperature rise in the material of the preform ata rate of 120° C./sec to 250° C./sec to reach an annealing temperaturein the range of 65% to 98% of the melting point temperature of thematerial of the preform; fluid pressure forming the annealed preform ina mold with a mold cavity defining the desired shape by pressurizing thepreform to expand the preform into contact with the mold cavity forimparting the desired shape onto the preform; and removing the resultingmolded container in the desired shape from the mold.
 2. The method ofclaim 1, wherein the metal preform is shock annealed prior to insertioninto the mold.
 3. The method of claim 2, comprising applying and curinga coating on at least one of an interior surface of the preform and anexterior surface of the preform after the shock annealing and prior tothe fluid pressure forming, to create a coated preform.
 4. The method ofclaim 3, further comprising differentially preheating the coatedpreform, or the coated preform after a necking operation, prior to thefluid pressure forming.
 5. The method of claim 4, wherein the preform isa coated preform having a coating on at least one of the interior andexterior surfaces, which coating has a temperature tolerance limit abovewhich heat damage to the coating occurs, wherein the preheatingtemperature is selected to be up to 50% above the tolerance limit andthe treatment time is selected to be less than 2 sec.
 6. The method ofclaim 5, wherein the preform is expanded in at least one region by 25%to 50% during the pressure forming.
 7. The method of claim 1, whereinthe preform is an extruded preform having been impact extruded from analuminum slug.
 8. The method of claim 1, wherein the fluid pressureforming comprises: placing the preform in the mold having an interiorshape complementary to the desired shape of the container and a moldbase movable between a loading position and a molded position;pressurizing the preform with pressurized fluid for expanding at leastone of a first portion of a sidewall of the preform and a portion of thepreform closed end into contact with the mold; and moving the mold basefrom the loading position to the molded position to form the preformclosed end into an inwardly concave shape.
 9. The method of claim 8,wherein the sidewall of the preform having a first diameter is expandedin a single pressure forming step (a) to achieve an overall shape of thecontainer and a second diameter 25% to 50% larger than the firstdiameter, and (b) to generate a three-dimensional relief structure inthe expanded sidewall, the three dimensional relief structure includingat least one relief feature deformed from the sidewall to a relativeelevation of 0.1% to 10% of the second diameter at the location of therelief feature, the relief feature including at least one edge with abending radius of 0.3 mm to 5 mm.
 10. The method of claim 9, wherein therelief feature is one of a protrusion and a recess.
 11. The method ofclaim 8, further comprising differentially preheating the preform priorto the fluid pressure forming.
 12. The method of claim 8, wherein thepreform includes an alignment recess in an external surface of theclosed end and the mold base comprises an alignment protrusion forengagement therewith during the pressure forming, for maintaining thepreform centered within the mold.
 13. The method of claim 1, wherein thegenerating the electromagnetic field comprises generating theelectro-magnetic field for exposing the material of the preform to apower density of 25 W/cm² to 100 W/cm² of preform surface area.
 14. Themethod of claim 13, wherein the electro-magnetic field has a frequencyin the range of 10 kHz to 600 kHz.
 15. The method of claim 13, whereinthe at least one region of the preform is shock annealed for a treatmenttime of 0.3 sec to 4 sec.
 16. The method of claim 1, wherein at leastfirst and second regions of the preform are differentially shockannealed by sequentially inductively heating the first and secondregions.
 17. The method of claim 16, wherein the first and secondregions are sequentially exposed to one or more electro-magnetic fieldsof equal or differing strength by moving at least one or both of thepreform and the one or more fields relative to one another.
 18. Themethod of claim 1, wherein the annealing temperature is in the range of425 to 550° C.
 19. A method of pressure molding a shaped metal containerof a desired shape from a metal preform having a cylindrical body withan open end and a closed end, the method comprising: generating anelectro-magnetic field; shock annealing at least one region of the metalpreform by exposing the preform to the electro-magnetic field forinductively heating material of the preform to generate a temperaturerise in the material of the preform of at least 120° C./sec to reach anannealing temperature in the range of 65% to 98% of the melting pointtemperature of the material of the preform; subsequently applying andcuring a coating on at least one of an interior surface of the preformand an exterior surface of the preform, to create a coated preform;differentially preheating the coated preform, wherein the differentiallypreheating the coated preform comprises sequentially inductively heatingfirst and second regions of the coated preform with an electro-magneticfield by sequentially exposing the first and second regions to theelectro-magnetic field by moving at least one or both of the coatedpreform and the field relative to one another; subsequently fluidpressure forming the coated preform in a mold with a mold cavitydefining the desired shape by pressurizing the coated preform to expandthe coated preform into contact with the mold cavity for imparting thedesired shape onto the coated preform, wherein at least one of the firstand second regions is subject to elevated three dimensional deformationduring the fluid pressure forming; removing the resulting moldedcontainer in the desired shape from the mold; and wherein the metalpreform is shock annealed prior to insertion into the mold.
 20. Themethod of claim 19, wherein the first and second regions are heated to apreheating temperature in the range of 100 to 300° C. and the first andsecond regions are heated for a treatment time of less than 4 sec. 21.The method of claim 19, wherein the inductively heating comprisesgenerating an electromagnetic field with a power input of 5 kW to 8 kW.22. The method of claim 21, wherein the electromagnetic field has afrequency in the range of 10 kHz to 600 kHz.
 23. The method of claim 19,wherein a necking operation is performed on the coated preform prior tothe differentially preheating.
 24. A method for annealing a metalpreform of a container, the preform having a sidewall, a closed end andan open end, the annealing method comprising: generating anelectro-magnetic field; and shock annealing at least one region of analuminum or aluminum alloy preform by exposing the preform to theelectro-magnetic field for inductively heating material of the preformto generate a temperature rise in the material of the preform at a rateof 120° C./sec to 250° C./sec to reach an annealing temperature in therange of 65% to 98% of the melting point temperature of the material ofthe preform.
 25. The method of claim 24, wherein the generating theelectromagnetic field comprises generating the electro-magnetic fieldfor exposing the material of the preform to a power density of 25 W/cm²to 100 W/cm² of preform surface area.
 26. The method of claim 25,wherein the electro-magnetic field has a frequency in the range of 10kHz to 600 kHz.
 27. The method of claim 25, wherein the at least oneregion of the preform is shock annealed for a treatment time of 0.3 secto 4 sec.
 28. The method of claim 24, wherein at least first and secondregions of the preform are differentially shock annealed by sequentiallyinductively heating the first and second regions.
 29. The method ofclaim 28, wherein the first and second regions are sequentially exposedto one or more electro-magnetic fields of equal or differing strength bymoving at least one or both of the preform and the one or more fieldsrelative to one another.
 30. The method of claim 24, wherein thealuminum or aluminum alloy preform is an impact extruded preform. 31.The method of claim 24, wherein the annealing temperature is in therange of 425 to 550° C.